The aim of the in vitro study was to examine the accumulation of Streptococcus mutans on light-cured composite materials and amalgam. Bacteria cultures were grown in a brain heart infusion medium, and their growth rate was determined through turbidity measurements. The data, so obtained, were evaluated statistically by analysis of variance (ANOVA) followed by Scheffe test. Experiments on amalgam showed better results compared to those on composite materials. There were no statistically significant differences in plaque accumulation on different composite materials after finishing and polishing procedures, compared to plaque accumulation on composite materials against a Mylar strip.